1. Field of the Invention
The present invention relates generally to the field of wastewater treatment. More specifically, the present invention relates to a method and system for controlling filtration wastewater treatment plants. Yet more specifically, the present invention relates to a method and system for controlling wastewater treatment filtration to provide selective denitrification of at least one of the filter units of the filtration system. The present invention further relates to a method of selectively denitrifying at least one of the filters of a wastewater filtration system while simultaneously operating the remainder of the filtration system in the normal filtration mode.
2. Description of Related Art
The filtration systems used in conjunction with wastewater treatment typically comprise a reservoir or channel where the wastewater is retained prior to being treated. The wastewater can flow from the channel over a weir into a bank of filters that are generally located adjacent the channel. The filter units are designed to filter out and capture the waste from the wastewater and each filter unit usually is comprised of a large vessel containing one or more layers of filtration media. The filtration media usually consists of layers of particles where the particle diameter varies with each successive layer. The normal filtration mode involves pouring the wastewater into the filter unit, passing the wastewater through the layer(s) of filter media, and subsequently drawing out the treated water from the bottom of the filter unit. It is the intent that the layers of filter media capture and contain the waste from the wastewater and discharge clean/treated water from the bottom of the filter unit.
The primary function of the filter media during a normal filtering mode is to remove solid particles from the wastewater. Compounds other than solid particles however often reside in wastewater that need to be removed, such as nitrates and nitrites. These compounds can be removed from the wastewater by introducing microorganisms onto some or all layers of the filter media. These microorganisms should be capable of denitrifying the wastewater by converting the nitrates and nitrites within the wastewater into diatomic molecules, such as oxygen and nitrogen. Denitrification with microorganisms requires the addition of a conversion agent, a carbon source for example, to the wastewater as well as reducing the magnitude of the wastewater flow through the filter.
The current practice in operating filtration systems requires that, during the denitrification mode, the conversion agent is added to the entire flow of wastewater being fed to the filtration system. Thus all filters within the filtration system go into the denitrification mode. Conversion agents such as methanol are costly. Sending all filters into a denitrification phase even though only few filters require it drives up the cost of the conversion agent.
Another problem with current practice occurs when a filtration system is being denitrified, that is that the entire wastewater flow rate can be reduced in order for denitrification to take place, thereby reducing the filtration capacity for the entire filter system during this phase. In some instances though, such as during a storm surge, the flow rate of the wastewater being treated cannot be reduced, and therefore if a particular filter unit within a filtration system requires denitrification, it must wait until wastewater demand flow rate is not at a peak level. Therefore, there exists a need for performing denitrification of a filtration system without noticeably affecting the wastewater treatment throughout the entire filtration system.